Infiniti G37S 2011 - battery issues?

Twice my battery has died on me after driving some distance. Both times the dealer kept it and said there was nothing wrong, said I just don’t drive it enough. Told me I need to drive 15 miles a day or leave it idling in my driveway for 20 mins to keep the battery revved up! The two times the battery went dead happened after some more significant driving. I left it in my garage for 2 weeks and came back, it was fine. This advice seems flawed…other ideas? I do drive the car most days and sometimes it is not 15 miles. Mileage is 20K now.

dealer checked charging system. of course. so your alt is good. you could get a new battery. and a battery tender device.

Clean battery terminals and grounds. Sounds as if the battery is draining while you drive. Clean and connections on alternator too. Check to make sure belts are tight and in good condition.